This invention relates to improvements in motor drive drive units particularly those which must be hand held in use. Such units have special advantage for drive of a flexible shaft of an internal vibrator or for that matter drive of any device which in use may be a source of electrical shock to the holder or manipulator of the drive unit.
Much time, money and labor has been applied in efforts to render drive units such as above described safer in use. Efforts have likewise been applied to render such units simpler in construction, easier to fabricate and assemble and adaptable to use in a variety of potentially dangerous environments and lighter in weight. While prior devices applied to similar purposes have been developed with some improvement in the area of concern, they have not been so designed as to satisfy the noted criteria, the target and achievement of embodiments of the present invention.
The prior art of which the present inventors are aware comprise the following U.S. Pats.:
Holther, Jr. U.S. Pat. No. 3,894,254, PA1 Mason, Jr. U.S. Pat. No. 3,188,054, PA1 Wyzenbeek U.S. Pat. No. 3,180,625, PA1 Pratt U.S. Pat. No. 3,344,291, PA1 Batson et al U.S. Pat. No. 3,462,623, PA1 Hult U.S. Pat. No. 3,760,209, PA1 Adair U.S. Pat. No. 4,059,898.